Okay, this isn't doable.
Now, changing the interface to show only the listings you want to see is doable, but the block chain is open to being looked at by everyone.
There is nothing hidden. It would take immense effort to hide it.
meaning, you would have to encrypt every post and then only decrypt the post for all the people "authorized" to view it.
So, most people just view their feed. And that is a list of people they follow. But, the bots and anyone who wants to, looks at the entire block chain. And everything is visible.
It should be if you just do it on the condenser level, right?
No, absolutely not.
You are asking for an intermediate layer, a layer between everyone and the blockchain that can be, will be used for censoring.
Hmm.. I don't think his idea is about censorship per se. He wants the option to publish in such a way where only his followers will see the post. So maybe it's a form of self-censorship? Something like this could be triggered by adding a special tag, similar to how the NSFW function works. If it's at the condenser level only, other condensers can simply choose not to implement it if they don't like the idea. In fact, STINC doesn't have to do this, anyone with a condenser can.
All the bots do not use a condenser.
So, most of what @frystikken wanted would be mute.
Else, the post is just one of thousands, the chances of being stumbled upon are minuscule.
The default (sorta) right now is that only your followers and the bots see your posts.
But, this doesn't end the problem. That of people outside of the group seeing and messing with the post. Thus, you would have to do something that breaks STEEM to implement this. And any such breaking ends up with a tool to censor.